Fix regression that caused tags to not be sorted when displayed in the book details panel. Fixes #1351622 [tags are not shown alphabetically in Book Details Window](https://bugs.launchpad.net/calibre/+bug/1351622)
Handle null values in mi.tags when formatting the tags field
Edit Book: Fix a regression that caused clicking on links in the preview panel that lead to destinations in the same HTML file popping up a spurious error message.
Port compiling of .ui forms
Port imports
Port build script for building PyQt extensions to PyQt5
Port the progress indicator extension to PyQt5
Allow controlling PyQt5 import path via the env var PYQT5_IMPORT_PATH
faster builds
Get rid of the PyQt4 string from everywhere
Port: setMargin() reset() QStringList()

setMargin(): QLayout no longer has a setMargin() function, replace with
setContentsMargins()

reset(): QAbstractListModel no longer has reset(), replace with
beginResetModel(), endResetModel()

QStringList: No longer exists, a simply python list of strings works
instead
Fix mouse wheel not working in diff view
Port coffeescript compiler
Add note about headless Qt QPA plugin
Port WebKit imports and QChar

WebKit has been split up into QtWebKit and QtWebKitWidgets. Change
imports accordingly.

Replace use of QChar since it no longer exists in PyQt5
Port syntax highlighters
note about creating import checker
...
Port usage of QString and various miscellaneous imports that no longer work
Port various import from QtGui to Qt